Measurement of the $ D^{0}\rightarrow K^{-}\pi^{+}e^{+}e^{-} $ branching fraction and search for $ D^{0}\rightarrow \pi^{+}\pi^{-}e^{+}e^{-} $ and $D^{0}\rightarrow K^{+}K^{-}e^{+}e^{-} $ decays at Belle

TL;DR

This paper measures the branching fraction of a rare $D^0$ decay involving electrons and searches for similar decays with different mesons, setting upper limits due to no significant signals found.

Contribution

First measurement of the $ D^{0} ightarrow K^{-} ightarrow ightarrow e^{+}e^{-} $ branching fraction and the first search for related decays with upper limits at the $10^{-7}$ level.

Findings

Branching fraction for $ D^{0} ightarrow K^{-} ightarrow e^{+}e^{-} $ is approximately 40 x 10^{-7}.

No significant signals for other decay modes; upper limits set at the $10^{-7}$ level.

Analysis based on 942 fb$^{-1}$ data collected by Belle.

Abstract

We present a study of the rare charm meson decays $ D^{0}\rightarrow K^{+}K^{-}e^{+}e^{-} $, $ \pi^{+}\pi^{-}e^{+}e^{-} $, and $ K^{-}\pi^{+}e^{+}e^{-} $ using a 942 fb$^{-1}$ data set collected by the Belle detector at the KEKB asymmetric-energy $ e^{+}e^{-} $ collider. We use $ D^{0} $ candidates identified by the charge of the pion in $ D^{*} \rightarrow D^{0} \pi $ decays and normalize the branching fractions to $ D^{0} \rightarrow K^{-}\pi^{+}\pi^{-}\pi^{+} $ decays. The branching fraction for decay $ D^{0} \rightarrow K^{-}\pi^{+}e^{+}e^{-} $ is measured to be (39.6 $\pm$ 4.5 (stat) $\pm$ 2.9 (syst)) $\times$ $10^{-7}$, with the dielectron mass in the $ \rho/\omega $ mass region $ 675 < m_{ee} < 875 $ MeV$/c^{2}$. We also search for $ D^{0}\rightarrow h^{-} h^{(\prime)+}e^{+}e^{-} $ ($ h^{(\prime)}=K,\,\pi $) decays with the dielectron mass near the $\eta$ and $\phi$ resonances, and away from these resonances for the $ K^{+}K^{-}e^{+}e^{-} $ and $ \pi^{+}\pi^{-}e^{+}e^{-} $ modes. For these modes, we find no significant signals and set 90$\%$ confidence level upper limits on their branching fractions at the $\mathcal{O}$(10$^{-7}$) level.